Implant planning for multiple implant components using constraints

ABSTRACT

Described are computer-based methods and apparatuses, including computer program products, for implant planning for multiple implant components using constraints. A representation of a bone and a representation of a first implant component are displayed with respect to the representation of the bone. A representation of a second implant component is displayed, wherein the first implant component and the second implant component are physically separated and not connected to each other. A positioning of the representation of the second implant component that violates at least one positioning constraint is prevented, wherein the positioning constraint is based on the representation of the first implant component.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/589,981, filed Aug. 20, 2012, which is a continuation of U.S.application Ser. No. 12/333,109, filed Dec. 11, 2008; U.S. applicationSer. No. 13/589,981 is also a continuation-in-part of U.S. applicationSer. No. 11/963,547, filed Dec. 21, 2007, which claims the benefit ofand priority to U.S. Provisional Application No. 60/925,269, filed Apr.19, 2007; all of which are hereby incorporated by reference herein intheir entireties.

FIELD OF THE INVENTION

The present invention relates generally to surgical computer systems,including computer program products, and methods for implant planningfor multiple implant components, particularly to multiple componentimplant constraints.

BACKGROUND

Orthopedic joint replacement surgery may involve arthroplasty of a knee,hip, or other joint (e.g., shoulder, elbow, wrist, ankle, fingers,etc.). For example, traditional total knee arthroplasty (TKA) involves along incision, typically in a range of about 6 to 12 inches, to exposethe joint for bone preparation and implantation of implant components.The invasive nature of the incision results in a lengthy recovery timefor the patient. Minimally invasive surgery (MIS) reduces the incisionlength for a total knee replacement surgery to a range of about 4 to 6inches. However, the smaller incision size reduces a surgeon's abilityto view and access the anatomy of a joint. Consequently, the complexityof assessing proper implant position and reshaping bone increases, andaccurate placement of implants may be more difficult. Inaccuratepositioning of implants compromises joint performance. For example, oneproblem with TKA is that one or more components of the implant mayimproperly contact the patella, which may be caused by inaccuratepositioning of the one or more implant components within the knee.

An important aspect of implant planning concerns variations inindividual anatomies. As a result of anatomical variation, there is nosingle implant design or orientation of implant components that providesan optimal solution for all patients. Conventional TKA systems typicallyinclude a femoral component that is implanted on the distal end of thefemur, a tibial component that is implanted on the proximal end of thetibia, and a patellar component that replaces the articular surface ofthe patella. As mentioned above, conventional TKA systems require anincision large enough to accept implantation of the femoral and tibialcomponents. Further, the femoral and tibial components have standard,fixed geometries and are only available in a limited range of sizes. Asa result, the surgeon may be unable to achieve a fit that addresses eachpatient's unique anatomy, ligament stability, and kinematics.

Modular TKA knee prostheses comprising multiple components that areinserted separately and assembled within the surgical site have beendeveloped to overcome conventional TKA systems. Some modular TKA systemimplementations mimic a conventional TKA system by allowing the multiplecomponents to be inserted separately so the components can be connectedtogether inside the patient's body. One disadvantage is that the modularcomponents, once assembled inside the patient's body, mimic aconventional TKA system and thus suffer from similar limitations. Oncethe modular components are fixed together, the components are dependentupon one another. Such implant systems do not enable the surgeon to varythe placement or geometry of each modular component to best suit eachpatient's unique anatomy, ligament stability, kinematics, and diseasestate.

Some modular TKA system implementations allow the implant components tobe positioned independently of one another. An example of independentcomponent placement systems and methods is described in U.S. patentapplication Ser. No. 11/684,514, filed Mar. 9, 2007, published as Pub.No. 2008/0058945, and hereby incorporated by reference herein in itsentirety. One disadvantage of such systems is the determination of theplacement of each implant component is not constrained based on theother implant components. Multiple component implant systems, however,often require that a number of relative constraints between thecomponents be satisfied so that the implant system functions properly.If all implants are planned independently, it is nearly impossible tosatisfy all the necessary constraints. For example, in order to have asmooth transition between the femoral condyle implant and the patellaimplant, the relative position of the two implants to each other iscritical.

Further, proper placement of the implant components on the femur andtibia require knowledge of the articular cartilage surfaces of eachbone. Articular cartilage is an avascular soft tissue that covers thearticulating bony ends of joints. During joint motion, cartilage acts asa lubricating mechanism in the articulating joints and protects theunderlying bony structure by minimizing peak contact force at the joint.A model of each bone can be generated from a CT scan of the bone toallow models of the implant components to be positioned relative to thebone models to plan for the surgery. However, CT scans may notaccurately determine the articular cartilage surface of the bone. As aresult, the planned placement of the implant components match only thesurface of the bone and not the cartilage, while the surface of thecartilage frequently determines the optimal placement of the implant.Cartilage surfaces can be determined by capturing the tip positions of atracked probe while the probe is dragged over the cartilage surface.However, this requires that each point is captured to draw the cartilagesurface, which is a timely and computationally involved procedure.

In view of the foregoing, a need exists for surgical methods and deviceswhich can overcome the aforementioned problems so as to enableintraoperative implant planning for accurate placement and implantationof multiple joint implant components providing improved jointperformance; consistent, predictable operative results regardless ofsurgical skill level; sparing healthy bone in minimally invasivesurgery; achieving a fit of the implant components that address eachpatient's unique anatomy, ligament stability, and kinematics; andreducing the need for replacement and revision surgery.

SUMMARY OF THE INVENTION

The techniques described herein provide methods, apparatuses, andcomputer program products for implant planning for multiple implantcomponents using constraints and implant planning using areasrepresenting cartilage. Such implant planning facilitates the accurateplacement of implant components of a multiple component implant to fitthe unique anatomy of a patient.

In one aspect there is a method. The method is a surgical planningcomputerized method for displaying a representation of a bone and arepresentation of a first implant component with respect to therepresentation of the bone. The method also includes displaying arepresentation of a second implant component, wherein the first implantcomponent and the second implant component are physically separated andnot connected to each other. The method also includes preventing apositioning of the representation of the second implant component thatviolates at least one positioning constraint, wherein the positioningconstraint is based on the representation of the first implantcomponent.

In another aspect, there is a method. The method is a surgical planningcomputerized method for displaying a representation of a bone and arepresentation of a first implant component with respect to therepresentation of the bone. The method also includes receiving dataassociated with a positioning of a representation of a second implantcomponent, wherein the first implant component and the second implantcomponent are physically separated and not connected to each other. Themethod also includes comparing the data associated with the positioningof the representation of the second implant component with a positioningconstraint that is based on the representation of the bone, therepresentation of the first implant component, or both. The method alsoincludes displaying the representation of the second implant componentin accord with the data associated with the positioning of therepresentation of the second implant component if the data meets thepositioning constraint.

In another aspect, there is a system. The system is a surgical planningsystem including a computer configured to generate a display of arepresentation of a bone and a representation of a first implantcomponent with respect to the representation of the bone. The computeris also configured to generate a display of a representation of a secondimplant component, wherein the first implant component and the secondimplant component are physically separated and not connected to eachother. The computer is also configured to prevent a positioning of therepresentation of the second implant component that violates at leastone positioning constraint, wherein the positioning constraint is basedon the representation of the first implant component.

In another aspect, there is a computer program product. The computerprogram product is tangibly embodied in a computer readable medium. Thecomputer program product includes instructions being operable to cause adata processing apparatus to display a representation of a bone and arepresentation of a first implant component with respect to therepresentation of the bone. The instructions are also operable to causea data processing apparatus to display a representation of a secondimplant component, wherein the first implant component and the secondimplant component are physically separated and not connected to eachother. The instructions are also operable to cause a data processingapparatus to prevent a positioning of the representation of the secondimplant component that violates at least one positioning constraint,wherein the positioning constraint is based on the representation of thefirst implant component.

In another aspect, there is a system. The system includes displaying arepresentation of a bone and a representation of a first implantcomponent with respect to the representation of the bone. The systemalso includes displaying a representation of a second implant component,wherein the first implant component and the second implant component arephysically separated and not connected to each other. The system alsoincludes means for preventing a positioning of the representation of thesecond implant component that violates at least one positioningconstraint, wherein the positioning constraint is based on therepresentation of the first implant component.

In another aspect, there is a method. The method is a surgical planningcomputerized method for determining a predetermined number of controlpoints for generating a predetermined number of areas representingcartilage, wherein the predetermined number of control points are basedon an implant component. The method also includes receiving measurementscorresponding to a plurality of measured cartilage points, wherein eachcartilage point is based on an associated control point from thepredetermined number of control points. The method also includesgenerating a plurality of areas representing cartilage, wherein eacharea representing cartilage is larger than and projects to an associatedcontrol point from the plurality of control points. The method alsoincludes positioning a representation of the implant component based ona representation of a bone, the representation of the bone comprisingrepresentations of the plurality of areas representing cartilage.

In another aspect, there is a system. The system is a surgical planningsystem including a computer configured to determine a predeterminednumber of control points for generating a predetermined number of areasrepresenting cartilage, wherein the predetermined number of controlpoints are based on an implant component. The computer is furtherconfigured to generate a plurality of areas representing cartilage,wherein each area representing cartilage is larger than and projects toan associated control point from a plurality of control points. Thecomputer is further configured to position a representation of theimplant component based on a representation of a bone, therepresentation of the bone comprising the plurality of areasrepresenting cartilage. The system also includes a probe configured tomeasure the plurality of cartilage points, wherein each cartilage pointis based on an associated control point from the predetermined number ofcontrol points.

In another aspect, there is a computer program product. The computerprogram product is tangibly embodied in a computer readable medium. Thecomputer program product includes instructions being operable to cause adata processing apparatus to determine a predetermined number of controlpoints for generating a predetermined number of areas representingcartilage, wherein the predetermined number of control points are basedon an implant component. The computer program product also includesinstructions being operable to cause a data processing apparatus toreceive measurements corresponding to a plurality of measured cartilagepoints, wherein each cartilage point is based on an associated controlpoint from the predetermined number of control points. The computerprogram product also includes instructions being operable to cause adata processing apparatus to generate a plurality of areas representingcartilage, wherein each area representing cartilage is larger than andprojects to an associated control point from the plurality of controlpoints. The computer program product includes instructions beingoperable to cause a data processing apparatus to position arepresentation of the implant component based on a representation of abone, the representation of the bone comprising representations of theplurality of areas representing cartilage.

In another aspect, there is a system. The system includes means fordetermining a predetermined number of control points for generating apredetermined number of areas representing cartilage, wherein thepredetermined number of control points are based on an implantcomponent. The system also includes means for receiving measurementscorresponding to a plurality of measured cartilage points, wherein eachcartilage point is based on an associated control point from thepredetermined number of control points. The system also includes meansfor generating a plurality of areas representing cartilage, wherein eacharea representing cartilage is larger than and projects to an associatedcontrol point from the plurality of control points. The system alsoincludes means for positioning a representation of the implant componentbased on a representation of a bone, the representation of the bonecomprising representations of the plurality of areas representingcartilage.

In other examples, any of the aspects above can include one or more ofthe following features. A plurality of areas representing cartilage canbe calculated, and a positioning of the representation of the firstimplant component that violates a second positioning constraint that isbased on the plurality of areas representing cartilage can be prevented.The at least one positioning constraint can include a rigid constraintbetween the representation of the first implant component and therepresentation of the second implant component, wherein the rigidconstraint prevents a positioning of the representation of the secondimplant component that is independent of the representation of the firstimplant component.

In some examples, the at least one positioning constraint comprises oneor more axes of movement of the representation of the second implantcomponent based on the representation of the first implant component. Anaxis from the one or more axes can constrain a critical area between therepresentation of the first implant component and the representation ofthe second implant component. An axis from the one or more axes canconstrain a distance between the representation of the first implantcomponent and the representation of the second implant component. Anaxis from the one or more axes can be based on an arc between therepresentation of the first implant component and the representation ofthe second implant component.

In other examples, preventing comprises preventing a movement of therepresentation of the second component that is not a rotation around theone or more axes, a translation along the one or more axes, or anycombination thereof. A cross-sectional display can be displayed at across-section point along an axis from the one or more axes, wherein thecross-sectional display comprises the representation of the firstimplant component, the representation of the second implant component,the representation of the bone, or any combination thereof. Thecross-sectional display can be updated based on a new cross-sectionpoint along the axis.

In some examples, the at least one positioning constraint is based on arepresentation of an extension of an articular surface of at least oneof the first implant component and the second implant component. Anoverlap of the representation of the extension of the articular surfaceand the representation of the first implant component, therepresentation of the second implant component, or any combinationthereof can be determined. The representation of the extension of thearticular surface can be displayed. Displaying the representation of thesecond implant component can include displaying the representation ofthe second implant component with respect to the representation of thebone.

In other examples, displaying the representation of the second implantcomponent with respect to the representation of the bone furthercomprises displaying the representation of the second implant componentbased on at least one of a coordinate space of the representation of thebone or a coordinate space of the representation of the first implantcomponent. A change indicator can be displayed, wherein the changeindicator is based on a current location of the representation of thefirst implant component and at least one of an original location of therepresentation of the first implant component, a coordinate space of therepresentation of the bone, a coordinate space of the representation ofthe first implant component, or a coordinate space of a representationof cartilage. Data associated with a positioning of the representationof the second implant component can be received.

In some examples, the computer is further configured to generate a userinterface that enables a positioning of either the representation of thefirst implant component, the representation of the second implantcomponent, or any combination thereof. The computer can be furtherconfigured to calculate a plurality of areas representing cartilage andto adjust a positioning of at least one of the representation of thefirst implant component and the representation of the second implantcomponent based on at least one of the plurality of areas representingcartilage. The representation of the implant component can beautomatically aligned to fit the plurality of areas representingcartilage.

In other examples, generating the plurality of areas representingcartilage includes transforming the predetermined number of controlpoints to a coordinate space of the representation of the bone andtransforming the plurality of cartilage points to the coordinate spaceof the representation of the bone. Generating the plurality of areasrepresenting cartilage can include, for each area representing cartilagefrom the plurality of areas, calculating a distance between a point ofthe representation of the bone and an associated transformed cartilagepoint, calculating a direction between a closest point of therepresentation of the bone to an associated transformed control point,determining a plurality of points of the representation of the bone thatare within a second distance from the associated transformed controlpoint, and adjusting the plurality of points based on the seconddistance and direction to form the plurality of areas representingcartilage.

In some examples, each of the plurality of points of the representationof the bone corresponds to a set of polygons from a superset ofpolygons, the representation of the bone comprising the superset ofpolygons. Adjusting can include adjusting a vertex of each polygon fromthe set of polygons. The superset of polygons can include triangles.Calculating the distance between the point of the representation of thebone and the associated transformed cartilage point can includeselecting a closest point of the representation of the bone to theassociated transformed cartilage point.

In other examples, for each area representing cartilage of the pluralityof areas representing cartilage, registering a control point from thetransformed predetermined number of control points to a closest point inthe area representing cartilage. The registered control point can beconstrained to automatically adjust a position of the representation ofthe implant component. The representation of the bone can be displayed,and the representation of the implant component with respect to therepresentation of the bone can be displayed. A representation of asecond implant component can be displayed, wherein the implant componentand the second implant component are components of a multiple componentimplant. The method can include determining if a positioning of therepresentation of the second implant component violates at least onepositioning constraint.

In some examples, the at least one positioning constraint is based onthe representation of the bone, the representation of the implantcomponent, or any combination thereof. The computer can be furtherconfigured to generate a display of a second implant component, whereinthe implant component and second implant component are components of amultiple component implant. The computer can be further configured todetermine if a positioning of the representation of the second implantcomponent violates at least one positioning constraint. The at least onepositioning constraint can be based on the representation of the bone,the representation of the implant component, or both. The computer canbe further configured to generate a user interface that enables apositioning of either the representation of the implant component, therepresentation of the second implant component, or any combinationthereof.

The techniques for implant planning for multiple implant componentsusing constraints and implant planning using areas representingcartilage described herein can provide one or more of the followingadvantages. Since each patient's anatomy is unique, having multiplesizes and shapes for the implant components and constraining thepositioning of the components with respect to other components and/orthe bone allows the system to find a best fit for each patient. Theconstraints provide information on positioning the components accuratelyand effectively, preventing improper placement, and enabling themultiple components of the implant to work with each other as they weredesigned to do so. Multiple types of visual displays further enhanceproper placement of the implant components. Further, implant componentscan be adjusted to account for cartilage representations. A moreeffective, less intrusive implant planning procedure can be achieved foreach individual patient. Implant planning using constraints allows theplacement of components that are physically separated and not touchingto be optimally placed within a patient's anatomy at locations whichensure the components operate as designed. Optimal positioning ofsmaller, separate components allows for smaller incisions (e.g., due tothe smaller components) and less invasive surgeries.

Other aspects and advantages of the present invention will becomeapparent from the following detailed description, taken in conjunctionwith the accompanying drawings, illustrating the principles of theinvention by way of example only.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features, and advantages of the presentinvention, as well as the invention itself, will be more fullyunderstood from the following description of various embodiments, whenread together with the accompanying drawings.

FIG. 1 illustrates an exemplary multiple component implant planningsystem according to the present invention;

FIG. 2 is a perspective view of a femur and representations ofcomponents of an exemplary multiple component implant as presented bythe display of FIG. 1;

FIG. 3 illustrates an exemplary method for implant planning withconstraints for components of a multiple component implant;

FIG. 4A illustrates a prospective display including constraints forrepresentations of components of a multiple component implant;

FIG. 4B illustrates a cross-sectional display along a constraint axisincluding representations of components of a multiple component implant;

FIG. 5 illustrates a split display including constraints forrepresentations of components of a multiple component implant;

FIG. 6 illustrates a split display including cartilage areas along arepresentation of a bone;

FIG. 7 illustrates an exemplary method for positioning an implantcomponent based on areas representing cartilage;

FIG. 8 illustrates an exemplary method for estimating areas representingcartilage;

FIGS. 9A-9D illustrate bone points on a femur for implant planning;

FIGS. 10A-10C illustrate implant points on implant components of amultiple component implant for implant planning;

FIGS. 11A-11C illustrate implant component axes relative to implantcomponents of a multiple component implant for implant planning; and

FIG. 12 shows an embodiment of an exemplary surgical computer system forimplant planning using constraints and/or areas representing cartilage.

DETAILED DESCRIPTION

Presently preferred embodiments are illustrated in the drawings.Although this specification refers primarily to knee joint replacementsurgery, it should be understood that the subject matter describedherein is applicable to other joints in the body, such as, for example,a shoulder, elbow, wrist, spine, hip, or ankle and to any otherorthopedic and/or musculoskeletal implant, including implants ofconventional materials and more exotic implants, such as orthobiologics,drug delivery implants, and cell delivery implants.

In general overview, multiple component implant planning is achieved byconstraining the adjustment of the individual components of the multiplecomponent implant. Each component can be adjusted based on theconstraints, allowing a proper fit for each implant component whilepreventing improper placement. FIG. 1 illustrates an exemplary multiplecomponent implant planning system 100 according to the presentinvention. The system includes computer 102. Computer 102 is incommunication with input unit 104. Input unit 104 is in communicationwith probe 106. Computer 102 is further in communication with display108.

The computer 102 may be any known computing system but is preferably aprogrammable, processor-based system. For example, the computer 102 mayinclude a microprocessor, a hard drive, random access memory (RAM), readonly memory (ROM), input/output (I/O) circuitry, and any otherwell-known computer component. The computer 102 is preferably adaptedfor use with various types of storage devices (persistent andremovable), such as, for example, a portable drive, magnetic storage(e.g., a floppy disk), solid state storage (e.g., a flash memory card),optical storage (e.g., a compact disc or CD), and/or network/Internetstorage. The computer 102 may comprise one or more computers, including,for example, a personal computer (e.g., an IBM-PC compatible computer)or a workstation (e.g., a SUN or Silicon Graphics workstation) operatingunder a Windows, MS-DOS, UNIX, or other suitable operating system andpreferably includes a graphical user interface (GUI).

The input unit 104 enables information to be communicated to the implantplanning system 100. For example, the input unit 104 provides aninterface for a user to communicate with the implant planning system.The terms user and operator both refer to a person using the implantplanning system 100 and are sometimes used interchangeably. The inputunit 104 is connected to the computer 102 and may include any deviceenabling a user to provide input to a computer. For example, the inputunit 104 can include a known input device, such as a keyboard, a mouse,a trackball, a touch screen, a touch pad, voice recognition hardware,dials, switches, buttons, a trackable probe, a foot pedal, a remotecontrol device, a scanner, a camera, a microphone, and/or a joystick.The input unit 104 may also include surgical navigation equipment thatprovides data to the computer 102. For example, the input unit 104 caninclude a tracking system for tracking the position of surgical toolsand patient anatomy. The tracking system may be, for example, anoptical, electromagnetic, radio, acoustic, mechanical, or fiber optictracking system.

The probe 106 may be any probe for measuring the thickness of articularcartilage. An example of a probe is U.S. Pat. No. 6,585,666 (“the '666patent”), filed Jul. 30, 2001, and incorporated by reference herein inits entirety. The '666 patent discloses a diagnostic probe whichdetermines the thickness of articular cartilage as a function of thetrue ultrasound speed of the cartilage. The probe 106 may also be atracked probe, where tip positions of the probe are captured (e.g., byan optical camera, joint encoders, etc.) when the probe tip is touchedto the cartilage surface. Because the patient's bones are inregistration with bone models (created, for example, from CT scans ofthe bones), the captured tip positions can be compared to the knownlocation of the bone surface to estimate the thickness of the cartilage.The tracked probe may be, for example, a probe having optical markersaffixed thereto or an end effector of an articulated or robotic arm.

The probe 106 is in operative communication with the computer 102. Forexample, the probe 106 may be coupled to the computer 102 via aninterface (not shown). The interface can include a physical interfaceand/or a software interface. The physical interface may be any knowninterface such as, for example, a wired interface (e.g., serial, USB,Ethernet, CAN bus, and/or other cable communication interface) and/or awireless interface (e.g., wireless Ethernet, wireless serial, infrared,and/or other wireless communication system). The software interface maybe resident on the computer 102. For example, in the case of a trackedprobe that includes optical markers, probe tip position data is capturedand relayed to the computer 102 by an optical camera.

The display 108 is a visual interface between the computer 102 and theuser. The display 108 is connected to the computer 102 and may be anydevice suitable for displaying text, images, graphics, and/or othervisual output. For example, the display 108 may include a standarddisplay screen (e.g., LCD, CRT, plasma, etc.), a touch screen, awearable display (e.g., eyewear such as glasses or goggles), aprojection display, a head-mounted display, a holographic display,and/or any other visual output device. The display 108 may be disposedon or near the computer 102 (e.g., mounted within a cabinet alsocomprising the computer 102) or may be remote from the computer 102(e.g., mounted on a wall of an operating room or other location suitablefor viewing by the user). The display 108 is preferably adjustable sothat the user can position/reposition the display 108 as needed during asurgical procedure. For example, the display 108 may be disposed on anadjustable arm (not shown) or on any other location well-suited for easeof viewing by the user. The display 108 may be used to display anyinformation useful for a medical procedure, such as, for example, imagesof anatomy generated from an image data set obtained using conventionalimaging techniques, graphical models (e.g., CAD models of implants,instruments, anatomy, etc.), graphical representations of a trackedobject (e.g., anatomy, tools, implants, etc.), digital or video images,registration information, calibration information, patient data, userdata, measurement data, software menus, selection buttons, statusinformation, and the like. The terms model and representation can beused interchangeably to refer to any computerized display of a component(e.g., implant, bone, tissue, etc.) of interest.

In some embodiments, the display 108 displays graphical representationsof the bones associated with a joint of interest (e.g., the femur andtibia of a knee joint). The display 108 can further display graphicalrepresentations of one or more components of a multiple componentimplant. FIG. 2 is a perspective view 150 of a representation of a femur152 and representations of components of an exemplary multiple componentimplant as presented by the display 108 of FIG. 1. The representation ofthe multiple component implant includes a central patello-femoralimplant component 154 and a medial implant component 156. Therepresentation of the multiple component implant may further include alateral implant component 158. The display 108 can allow a user toposition one or more of the implant component representations (e.g., thepatello-femoral implant component 154, the medial implant component 156,and/or the lateral implant component 158). The positioning of therepresentations of the implant components can be based on constraints,as will be discussed further below. The representations of componentsand/or bones can be semi-transparent to demonstrate the relationshipamong the components and/or bones. For example, in FIG. 2, therepresentation of the femur 152 is semi-transparent so the portions ofboth the medial implant component 156 and the lateral implant component158 located under the representation of the femur 152, which wouldnormally be hidden, can be viewed by a user of the implant planningsystem 100.

The components of the multiple component implant are preferablysegmented components. As shown in FIG. 2, a segmented component is anindividual component implanted on the bone as an independent,self-contained, stand-alone component that is not physically constrainedby any other component of the multiple component implant (as usedherein, the term physically constrained means that the components arelinked through a physical connection and/or physical contact in such amanner that the link between the components imposes limitations on thepositioning or placement of either of the components). Thus, therepresentation of the patello-femoral implant component 154, therepresentation of the medial implant component 156, and therepresentation of the lateral implant component 158 are all segmentedcomponents. To ensure that a segmented component is not physicallyconstrained by other components, the segmented component may beimplanted in the joint so that the component is not connected to and/orin contact with any other segmented component.

For example, the components of the multiple component implant areconfigured such that the components can be implanted on a patient'sfemur without being connected, as shown in FIG. 2. While FIG. 2 shows agraphical representation of both the implant components and the bone,the representations of the implant components and the bone areindicative of the actual implantation of the implant components on apatient's bone as represented by FIG. 2. For example, for perspectiveview 150, the representation of the patello-femoral implant component154, the representation of the medial implant component 156, and therepresentation of the lateral implant component 158 are notinterconnected when fixed relative to the representation of the femur152. Similarly, during the actual implant procedure for the implantcomponents, the patello-femoral implant component, the medial implantcomponent, and the lateral implant component are not interconnected whenfixed relative to the patient's femur. Providing perspective view 150(e.g., through display 108 of the implant planning system 100)advantageously allows a user to plan the implant procedure before apatient surgery to maximize the effectiveness of the implant whileminimizing the invasiveness of the surgery to the patient.

For example, the system of three implant components (e.g., components154, 156, and 158) can be rotated and translated as one rigidly attachedsystem to an initial location in the joint. The initial location canmatch the representation of the implant to the representation of one ormore bones and/or the representation of the cartilage surface on the oneor more bones. For example, FIG. 2 shows the representations of thethree implant components aligned on the representation of the femur 152.Once the overall location and orientation have been set, individualcomponents (e.g., the medial implant component 156) can be rotatedaround one or more predefined axes. The axes can be defined, forexample, in the coordinate space of a reference componentrepresentation, the representation of the bone, or any other displayedrepresentation (e.g., the axes can be defined in the coordinate space ofthe central patello-femoral implant component 154).

In some embodiments the graphical displays are configured to provide foreasy identification of different items within the display. Items can bevisually distinguished from other items in the display through visualaids, such as color-coding, hatching, and shading. In some embodiments,all the representations of components of a multiple component implantare displayed with the same visual aid. In some embodiments, therepresentation of the bone and each implant component representation isdisplayed with a unique visual aid to facilitate easy identification ofthe implant component and the bone representations.

The graphical displays are used to provide the user with a simulation ofpositioning the implant components on a patient's anatomypreoperatively. The bone representation and implant componentrepresentations can be generated to the scale of the true component/bonerelative sizes and shapes. Advantageously, the implant componentrepresentations can be positioned (e.g., by an operator) on the bonerepresentation, and the bone representation can be moved to mimic actualposition changes of the bone that would occur post-operatively as thejoint moves through a range of motion, as described, for example, inU.S. patent application Ser. No. 11/963,547, filed Dec. 21, 2007, andhereby incorporated by reference herein in its entirety. An operator canthen adjust the implant component representations to find an optimalpositioning of the implant components along the bone prior to surgery.

FIG. 3 illustrates an exemplary method 200 for implant planning withconstraints for components of a multiple component implant, which willbe explained with reference to FIG. 2. The system (e.g., the implantplanning system 100 of FIG. 1) displays (202) a representation of a bone(e.g., on display 108). For example, the system displays athree-dimensional representation of the femur 152 (i.e., athree-dimensional graphical model of a patient's bone). The displayedbone representation can also be a two-dimensional representation. Forexample, the bone representation can be a cross-sectional representationof the bone. The graphical model of the bone may be generated in variousways. For example, as described in U.S. patent application Ser. No.12/147,997, filed Jun. 27, 2008, and hereby incorporated by referenceherein in its entirety, multiple sequential images of a patient'sanatomy are segmented to discern the outline of the anatomy andpropagated to adjacent images to generate a three-dimensional model ofthe patient's anatomy. Alternatively, for 3D imageless planning, boneatlases may be used to obtain the 3D bone models. A bone atlas is astatistical model that represents the relevant anatomy, includinginformation on natural variations typically existing in specificpopulations with specific distributions and probabilities. Using knownimage processing techniques and statistical data, the bone atlas may betransformed or “morphed” to find a best fit to the patient's anatomybased on demographic information, such as gender, age, stage of disease,and other patient-specific characteristics. Additionally, althoughpreoperative planning can be accomplished using the initial bone atlasmodel, once intra-operative registration data on the actual physicalbones is obtained, the bone atlas can be further morphed to improve thefit to the patient's anatomy along with corresponding adjustments to theimplant plan. The system displays (204) a representation of at least afirst implant component with respect to the bone. For example, thesystem displays the central patello-femoral implant component 154 withrespect to the representation of the femur 152. The system and/oroperator can position the implant component representation with respectto a base planning coordinate space. The base planning coordinate spacecan be, for example, the coordinate space of the representation of thebone. For CT image-based bone models, this corresponds to the coordinatespace of the CT scan of the patient's bone. Positioning by the operatorcan be accomplished using any input means (e.g., input unit 104, akeyboard, mouse, touch screen display, and/or the like).

The representation of an implant component can be a two-dimensionaland/or a three-dimensional model. The model can be stored on the implantplanning system 100. There can be multiple models for each component torepresent implant component systems of various sizes and shapes.Advantageously, since each patient's anatomy is unique, having multiplesizes and shapes for the implant components allows the system to find abest fit for each patient (e.g., based on bone shape and size, jointmovement, cartilage depth, and other physical characteristics unique tothe patient). For example, depending on the representation of the bone,the system and/or operator can choose a component system from aplurality of component systems that best fits the representation of thebone.

The system 100 displays (206) a representation of a second implantcomponent. For example, the system 100 displays medial implant component156. The system 100 receives (208) data associated with a positioning ofa representation of the second implant component. For example, anoperator can use the implant planning system 100 to adjust the multiplecomponent representations during an implant planning procedure tooptimize component placement for a patient. The operator can, forexample, reposition the medial implant component 156. The operator canreposition the medial implant component 156 using any input means (e.g.,input unit 104, a keyboard, mouse, touch screen display, and/or thelike). In some embodiments, steps 204 and 206 occur simultaneously. Forexample, the system displays the representations of the first and secondimplants, and the system and/or operator can position the implantcomponent representations with respect to the base planning coordinatespace. For example, the operator can rotate and/or translate themultiple implant components as one rigidly attached system to an initiallocation relative to the representation of the bone.

The system 100 determines (210) if the positioning of the representationof the second component violates at least one positioning constraint.Positioning constraints (see, e.g., FIG. 4A) allow an operator to movecomponent representations within certain limits to ensure, for example,the components operate properly, are non-intrusive to the patient'sanatomy, and are positioned correctly. Constraints can be associatedwith points, axes, lines, volumes, and/or other constraints. Forexample, constraints prevent an operator from positioning a componentrepresentation in an improper location. If the system 100 determines thepositioning of the representation of the second component violates apositioning constraint, the system 100 prevents (212) the positioning ofthe second implant component (e.g., the representation of the componenton the display will not move as requested by the input of the operator).If the system 100 determines the positioning does not violate thepositioning constraint, the system 100 allows (214) the new positioning.The system 100 can update the display to reflect the new positioning ofthe second implant component. In cases where the system 100 prevents thepositioning of the second implant, the system 100 can optionally providean error message to the operator indicating why the second implantcannot be moved to the desired position.

FIG. 4A illustrates a display 250 including constraints forrepresentations of components of a multiple component implant. Thedisplay 250 includes the representation of the femur 152, therepresentation of the patello-femoral implant component 154, and therepresentation of the medial implant component 156. The display 250includes three constraint axes, axes 252, 254, and 256. The constraintscan be visually distinguished from other items in the display throughvisual aids, such as color-coding, hatching, and shading. While thedisplay 250 includes three constraint axes, the display 250 can includeany number of constraint axes. Those skilled in the art can appreciatethat the constraints can be applied to any component of the multiplecomponent implant.

The constraint axes shown in FIG. 4A constrain the movement of themedial implant component 156 relative to the axes. The constraint axescan constrain the movement of the implant component based on one or moreother implant components, the representation of the bone, or arepresentation of cartilage (see, e.g., FIGS. 3-7). For example, theconstraint axes can constrain the movement of the medial implantcomponent 156 based on the patello-femoral implant component 154 or therepresentation of the femur 152.

The constraints can be axes of rotation and/or translation directionsdefined relative to any coordinate space (e.g., anatomic bone orimplant). In some embodiments, the constraint axes can be transformedfrom the implant coordinate space into the base planning coordinatespace (e.g., the coordinate space of the representation of the bone).For example, let

-   -   C_(B)=the base planning coordinate space;    -   C_(I1)=the coordinate space of a first (1) implant (I)        component;    -   C_(I2)=the coordinate space of a second (2) implant (I)        component;    -   T_(I1)=homogenous (rigid body) transformation matrix for the        transformation from the coordinate space of the first (1)        implant (I) component to the base planning coordinate space; and    -   T_(I2)=homogenous (rigid body) transformation matrix for the        transformation from the coordinate space of the second (2)        implant (I) component to the base planning coordinate space.

The rigid body transformation matrices perform translations whilepreserving Euclidean distances between coordinate locations. Homogeneouscoordinate transformation matrices operate on four-dimensionalhomogenous coordinate vector representations of traditionalthree-dimensional coordinate locations. Instead of representing eachpoint (x,y,z) in a three-dimensional space with a singlethree-dimensional vector:

$\begin{matrix}\begin{bmatrix}x \\y \\z\end{bmatrix} & {{Equation}\mspace{14mu} 1}\end{matrix}$homogenous coordinates allow each point (x,y,z) to be represented by anyof an infinite number of four dimensional vectors, which when multipliedby 1.0 results in the vector:

$\begin{matrix}\begin{bmatrix}x \\y \\z \\1.0\end{bmatrix} & {{Equation}\mspace{14mu} 2}\end{matrix}$The three-dimensional vector corresponding to any four-dimensionalvector can be computed by dividing the first three elements by thefourth, and a four-dimensional vector corresponding to anythree-dimensional vector can be created by simply adding a fourthelement and setting it equal to one. Any three-dimensional lineartransformation (e.g., rotation, translation, skew, and scaling) can berepresented by a 4×4 homogenous coordinate transformation matrix. Forexample, a translation can be represented by a 4×4 homogeneouscoordinate transformation matrix:

$\begin{matrix}\begin{bmatrix}1 & 0 & 0 & x_{s} \\0 & 1 & 1 & y_{s} \\0 & 0 & 1 & z_{s} \\0 & 0 & 0 & 1\end{bmatrix} & {{Equation}\mspace{14mu} 3}\end{matrix}$where:

-   -   x_(s)=translation along the x-axis;    -   y_(s)=translation along the y-axis; and    -   z_(s)=translation along the z-axis.

Multiplying Equation 1 by Equation 2 provides a transformation from athree-dimensional coordinate position (x,y,z) to the three-dimensionalcoordinate position (x′,y′,z′) as shown below:

$\begin{matrix}{\begin{bmatrix}x^{\prime} \\y^{\prime} \\z^{\prime} \\1.0\end{bmatrix} = {\begin{bmatrix}1 & 0 & 0 & x_{s} \\0 & 1 & 0 & y_{s} \\0 & 0 & 1 & z_{s} \\0 & 0 & 0 & 1\end{bmatrix}*\begin{bmatrix}x \\y \\z \\1.0\end{bmatrix}}} & {{Equation}\mspace{14mu} 4}\end{matrix}$

The first implant component is positioned from C_(I1) to C_(B) usingT_(I1). The second implant component is positioned from C_(I2) to C_(B)using T_(I2). To transform a point or vector defining a constraint fromC_(I1) to C_(I2) so that it can be used to limit the motion of thesecond implant component during planning, the point or vector ismultiplied by the homogeneous matrix, T_(I1)(T_(I2) ⁻¹), where T_(I2) ⁻¹is the inverse of T_(I2). In some examples, the homogeneous matrices canbe general transformations from one coordinate space to another.

The representation of the medial implant component 156 can bemanipulated based on the constraint axes 252, 254, and 256. For example,the medial implant component 156 can be rotated around the constraintaxes, translated along the constraint axes, and/or other movements sothat certain constraints (e.g., angles, distances, degrees of rotation,and/or the like) are preserved between the medial implant component 156and a base object (e.g., the representation of the femur 152 or therepresentation of the patello-femoral implant component 154). Forexample, a constraint axis can be defined as an axis which minimizes theeffect of the movement of the implant component with respect to a baseobject (i.e., the representation of the femur 152 or the representationof the patello-femoral implant component 154) for a known area that hasa substantial effect on the effectiveness of the overall multiplecomponent implant. By incorporating constraints into the implant system100, a user of the system 100 can freely position an implant componentrelative to a patient's bone in a way that does not compromise theeffectiveness of the multiple component implant. If the user attempts toposition the implant component in a location that could compromise theoperation of the implant system, the constraints automatically preventsuch positioning of the implant component. As such, the constraints actas an automatic guide for the user, ensuring eventual placement of animplant component that provides for a successful operation of themultiple component implant system.

Any number of constraint axes can be used. A constraint axis can bebased on an arc between the representation of a first implant componentand a representation of a second implant component. For example, if animplant component comprises an arc-like shape (e.g., the representationof the medial implant component 156 is shaped like an arc to properlyfit the rounded surface of the representation of the femur 152),constraints can be based on the arc to preserve a distance between theimplant component and other implant components. For example, constraintaxis 252 can be based on the arc center of the representation of themedial implant component 156.

A constraint axis can constrain a critical area between two implantcomponents (e.g., an area between the representation of the firstimplant component patello-femoral implant component 154 and therepresentation of the medial implant component 156). A critical regioncan be a region associated with two implant components that can have alarge effect on the overall operability of the multiple implantcomponent when one or more components of the multiple component implantare repositioned. For example, constraint axis 254 can be based on anarea between the representation of the patello-femoral implant component154 and the representation of the medial implant component 156 where thetwo implant components are within a critical distance (e.g., within 3 mmfrom touching). Axis 254 would constrain movement of the implantcomponents around the critical area to ensure proper positioning.

A constraint axis can constrain a distance between a representation of afirst implant component and a representation of a second implantcomponent. For example, constraint axis 256 can be selected as an axisbetween the representation of the patello-femoral implant component 154and the representation of the medial implant component 156 so thatmovement along axis 256 preserves the distance between therepresentation of the patello-femoral implant component 154 and therepresentation of the medial implant component 156. The axes can also beconstrained based on the representation of the bone (e.g., therepresentation of the femur 152), a representation of a cartilage area,and/or the like. Translational movements of implant componentrepresentations can also be constrained to two dimensions or anarbitrary plane. For example, one constraint is facilitating translationonly in the coronal or x/z plane. Another exemplary translationalconstraint is translation along an arbitrary curve in 3D space. Anotherexemplary constraint is to anchor the implant component to a specificpoint. For example, the specific point can be on or off the component,and can be identified in the coordinate system of a second component.For example, the implant can be “tied” to this specific point, butotherwise left unconstrained. Other constraints can include limiting thecomponent to one or more motions within a defined “bounding volume.” Forexample, a two or three-dimensional shape or area can represent the areawithin which a representation of an implant component can be moved.Movements which attempt to move the implant component outside of theshape or area can be prevented by the system.

Advantageously, displaying the constraint axes provides an operator(e.g., a surgeon) information on positioning the components of amultiple component implant accurately and effectively. For example,constraining the movement of the representation of the medial implantcomponent 156 along the three constraint axes 252, 254, 256 prevents theoperator from inadvertently positioning the medial implant component ina location which could be harmful to the patient's patella. Constraintscan be used to mirror factors related to the precise, accurate, andfunctional placement of the components, allowing an operator to safelyreposition the location of an implant component without jeopardizing thefunctionality of the implant. The operator need not know about thefactors, rather the factors are built into the system 100 throughconstraints. The operator is automatically prevented from moving thecomponent in a way which violates the constraints. This advantageouslyallows the multiple components to be placed according to the patient'sanatomy while still optimally working with each other as designed,without the operator having to know such details.

FIG. 4B illustrates a cross-sectional display 280 along a constraintaxis including representations of components of a multiple componentimplant. The cross-sectional display 280 is a cross-sectional view ofFIG. 4A along constraint axis 252. As such, the cross-sectional display280 is at a location of the three-dimensional display 250 so that theline representing constraint axis 252 is perpendicular to display 280(e.g., as if the viewer is looking straight down constraint axis 252 sothat constraint axis 252 appears only as a point). Those skilled in theart can appreciate that the cross-sectional display can be generatedabout any point of the three-dimensional display 250.

The cross-sectional display 280 includes the representation of the femur152. Because of the location of the cross-sectional display 280 withrespect to the three-dimensional display 250, the representation of thebone appears as two separate portions. Subsequent cross-sectional imagescan be generated along, for example, constraint axis 252 to portray theentire depth of the representation of the bone along constraint axis252. The cross-sectional display 280 includes the representation of thepatello-femoral implant component 154 and the representation of themedial implant component 156. The display 280 includes a portion of themedial implant component 156A located within the representation of thefemur 152. This can be, for example, a portion of the representation ofthe medial implant component 156 which protrudes into the representationof the femur 152 during the operation to affix the medial implantcomponent to the femur (e.g., a post or keel of the medial implantcomponent). The cross-sectional display 280 includes an outline of thesegmented bone surface 282. This outline matches the surface which isdisplayed in the 3D view (e.g., FIG. 4A). The outline of the segmentedbone surface 282 can be color-coded to facilitate easy identification(e.g., by a user). For example, the outline of the segmented bonesurface can be colored red.

In some embodiments, to constrain the rotation of an implant componentaround one axis (e.g., the representation of medial implant component156 about constraint axis 252), the representation of the bone and ofthe implant can be displayed in the cross-sectional display 280 alongthe constraint axis. Other movements of the implant component ofinterest besides movements for the implant component about theconstraint axis (e.g., transformations, rotations, and/or the like alongother constraint axes) can be disabled for the implant component. Thecross-sectional display can be scrolled along the rotation axis, whilethe center of rotation in the plane is fixed with respect to theconstraint axis. With respect to FIG. 4B, the medial implant component156 can be rotated around constraint axis 252, translated alongconstraint axis 252, and/or any other movement in relation to constraintaxis 252. In some embodiments, another constraint is that the range ofeach rotation can be limited. For example, the medial implant component156 can be constrained so it can be rotated around constraint axis 252within +/−15° from the current location of the medial implant component.

An implant component can be constrained along more than one axis. Forexample, to constrain the translation of the medial implant component156 along two axes (e.g., constraint axes 252 and 254), therepresentations of the bone and the implant component can be displayedin a two-dimensional display in which the plane is defined by the twoaxes. In some embodiments, the rotations can be disabled. In someembodiments, the translation in each two-dimensional display (e.g., eachdisplay based on two axes if multiple axes are present) can be limitedto one of the axis.

For any step of a surgical planning process, points, models or/andsurfaces can be displayed to facilitate the implant component planning.Like constraint axes, these points and surfaces can be defined in anarbitrary space (e.g., the coordinate space of one of the implantcomponents). FIG. 5 illustrates a split display 300 includingconstraints for representations of components of a multiple componentimplant. The split display 300 includes a three-dimensional display 302and a two-dimensional display 304. The display 300 includes an extensionsurface 306 and an extension surface 308, which are representations ofan extension of an articular surface. For example, as shown in FIG. 5,the extension surfaces 306 and 308 may each be a representation of anextension of a portion of the articular surface of the patello-femoralimplant component 154. Advantageously, providing both thethree-dimensional display 302 and the two-dimensional display 304 withthe extension surfaces 306, 308 can provide a user a reference for theideal placement of the implant component relative to the base object(e.g., the representation of the medial component 156 (implantcomponent) with respect to the representation of the patello-femoralcomponent 154 (base object)). In other examples, the femur 152 can bethe base object.

The three-dimensional display 302 includes the representation of thefemur 152. The three-dimensional display 302 includes the representationof the patello-femoral implant component 154 and the representation ofthe medial implant component 156. The three-dimensional display 302includes the extension surfaces 306, 308. The two-dimensional display304 includes the representation of the femur 152. The two-dimensionaldisplay 304 includes the representation of the patello-femoral implantcomponent 154 and the representation of the medial implant component156. The two-dimensional display 304 includes extension surfaces 306,308 and the outline of the segmented bone surface 282. This outlinematches the surface which is displayed in the 3D view. Thetwo-dimensional display includes a slider 310 and a change indicator312. The two-dimensional display 304 is a cross-sectional view of thethree-dimensional display. The slider 310 can move the two-dimensionaldisplay 304 along an axis which is perpendicular to thethree-dimensional display 302 to represent various 2D slices through thethree-dimensional display 302. The change indicator 312 can indicate thedifference between the coordinate system of a representation of animplant component with reference to a base reference. The base referencecan be, for example, an initial position of the representation of theimplant component, a base coordinate system (e.g., the coordinate systemof the representation of the bone, the coordinate system of therepresentation of a cartilage area), and any other reference point. Thechange indicator can represent a degree of change from the basereference, an angle of change from the base reference, a distance fromthe base reference, and any other metric between the representation ofthe implant component and the base reference. For example, the changeindicator 312 can display a degree of change between the currentlocation of the representation of the implant component and an originalrepresentation of the implant component.

The extension surfaces 306, 308 can be, for example, three-dimensionalshapes which are drawn between two implant components indicative of theoriginal placement of the two components. For example, the extensionsurfaces 306, 308 can be the surfaces which would connect the twoimplant components if the implant components were a single componentimplant. Movements of the implant components can be constrained by theextension surfaces 306, 308 based on the location of the implantcomponents relative to the extension surfaces 306, 308. Asrepresentations of the implant components are adjusted in the implantplanning system, the extension surfaces 306, 308 remain fixed based onthe original placement location of the implant components prior toadjustment. During adjustment of the implant components, the extensionsurfaces 306, 308 can be treated as transparent, allowing implantcomponents to “pass through” the extension surfaces 306, 308 if thecomponent is adjusted in a way that protrudes into the shape of theextension surfaces 306, 308. For example, moving the representation ofthe medial implant component 156 in one direction can cause therepresentation of the medial implant component 156 to protrude into therepresentation of extension surface 308. Similarly, moving therepresentation of the medial implant component 156 can cause a gap toform between the representation of extension surface 308 and therepresentation of the medial implant component 156. The overlap of theimplant components and the extension surfaces 306, 308, the distancebetween the implant components and the extension surfaces 306, 308, orboth can be used to constrain the movement of the implant componentsrelative to the extension surfaces 306, 308. Constraints can includelimiting the overlap between a representation of an implant componentand one or more corresponding extension surfaces, limiting the distancebetween a representation of an implant component and one or morecorresponding extension surfaces, and constraining other relationsbetween the implant components and the extension surfaces (e.g.,constraining rotations, translations, and/or the like between theimplant components and the extension surfaces).

FIG. 6 illustrates a split display 350 including cartilage areas along arepresentation of a bone. The split display 350 includes athree-dimensional display 352 and a two-dimensional display 354. Thethree-dimensional display 352 includes the representation of the femur152, the representation of the patello-femoral implant component 154,and the representation of the medial implant component 156. Thethree-dimensional display 352 includes cartilage points 356A, 356B, and356C (collectively, cartilage points 356). The three-dimensional display352 includes control points 358A, 358B, 358C and 358D (collectively,control points 358). The three-dimensional display 352 includes areasrepresenting cartilage 360A, 360B, 360C and 360D (collectively, areasrepresenting cartilage 360).

The two-dimensional display 354 includes the representation of the femur152, the representation of the patello-femoral implant component 154,and the representation of the medial implant component 156. Thetwo-dimensional display 354 includes cartilage points 356A, 356B, and356C. The three-dimensional display 352 includes control points 358A,358B, and 358C. The two-dimensional display includes a slider 310 and achange indicator 312 as discussed above with reference to FIG. 5.

FIG. 7 illustrates an exemplary process 400 for positioning an implantcomponent based on areas representing cartilage, using FIG. 6 as anexample. The representation of the femur 152 can be generated from a CTscan. In some examples, a CT scan only matches the surface of the bone,but not the surface of articular cartilage. In some embodiments, thesurface of the cartilage can be used to determine an optimal placementof an implant component. For example, the thickness of articularcartilage can be determined at critical places on the bone and used toposition the implant component. In some embodiments, a cartilage surfacecan be generated by capturing (e.g., with an optical camera) the tippositions of a tracked probe which is dragged over the cartilagesurface. The cartilage surface generated from the captured points can beused to manually or automatically position the implant component to theresulting surface. For example, to manually position the implantcomponent, the system 100 can display a representation of the cartilagesurface, and the user can manipulate the representation of the implantcomponent to achieve the desired placement of the implant componentsurface relative to the cartilage surface. In this example, a sufficientnumber of points are captured by the probe to generate a representationof the cartilage surface. Advantageously, cartilage thickness of thebone can be estimated over a region by lifting a patch of the bone modelto the estimated position. A predetermined number of control points 358are determined (402) based on the representation of the patello-femoralimplant component 154. The control points can be, for example, alongexterior edges of the implant component, at critical places of theimplant component, at the most exterior points of the component, anyother location along the implant component, or outside or off theimplant component surface but defined in the coordinate space of theimplant component. In this example, four control points are used. Inother examples, any number of control points can be used. Measurementsand/or calculations of the thickness and/or direction of cartilagepoints 356 are received (404), where each cartilage point is tied to anassociated control point from the control points 358. For example,cartilage point 356A is measured in proximity to control point 358A.Areas representing cartilage 360 are generated (406), wherein each arearepresenting cartilage is larger than and projects to the associatedcontrol point. For example, the area representing cartilage 360A islarger than and projects to control point 358A. For example, the systemcan assume the cartilage is about the same depth within a 10 mm diametercircle from a measurement point. Measuring one point allows an area of a10 mm diameter to be estimated on the bone model, rather thancalculating the entire cartilage area over the bone. Taking cartilagesurface measurements at predetermined locations near the control pointsallows the locations to coincide with the control points on the implantcomponent, making other cartilage portions on the bone irrelevant. Arepresentation of the patello-femoral implant component 154 ispositioned (408) based on the representation of the femur 152. Therepresentation of the femur 152 includes the areas representingcartilage 360.

In some examples, the areas representing cartilage 360 are formed fromadjusted points on the representation of the femur 152. Forming theareas representing cartilage 360 on the representation of the femur 152cause's protrusions along the representation of the femur 152. Thecontrol points 358 on the representation of the patello-femoral implantcomponent 154 can be used to reposition the patello-femoral implantcomponent 154 in the coordinate space of the implant system (e.g., thecoordinate space of the representation of the femur 152). For example,the patello-femoral implant component 154 can be repositioned away fromthe representation of the femur 152 so that the patello-femoral implantcomponent 154 is positioned adjacent to the representations of the areasrepresenting cartilage 360. Because the entire cartilage surface was notgenerated along the representation of the femur 152, this can result ina gap between the patello-femoral implant component 154 and therepresentation of the femur 152 where the patello-femoral implantcomponent 154 is not adjacent to the areas representing cartilage 360.In this case, points can be picked on the bone itself.

FIG. 8 illustrates an exemplary process (450) for estimating areasrepresenting cartilage. The surface of the cartilage is estimated atselected points by taking one cartilage measurement at locations on thepatient's cartilage that correspond to each control point and using theresulting distance and direction from the representation of the bone tocreate an area representing cartilage using the representation of thebone and the resulting offset. Using, for example, a tracked probe, anoperator captures cartilage points 356 on the patient in proximity toeach of the control points 358 of the selected implant (e.g., therepresentation of the patello-femoral implant 154). Take:

-   -   C_(B)=the coordinate space of the bone model;    -   C_(I)=the coordinate space of the implant;    -   C_(P)=the coordinate space of the patient;    -   T_(I)=the transformation from CI to CB; and    -   T_(P)=the transformation from CP to CB.

To estimate an area representing cartilage 360 at the position of eachcontrol point 358 relative to the representation of the femur 152, eachcartilage point 356 is transformed (452) to C_(B) using T_(P). Eachcontrol point 358 is transformed (454) to C_(B) using T_(I). The system100 determines the closest point on the representation of the femur 152to the transformed cartilage point 356. The system 100 calculates (456)the distance and direction from the closest point from therepresentation of the femur 152 to the transformed cartilage point 356.In some embodiments, the system 100 calculates a direction between aclosest points of the representation of the femur 152 to an associatedtransformed control point and uses the distance (cartilage thickness) ofthe transformed cartilage point 356 from the representation of the femur152. The system 100 determines (458) a plurality of points of therepresentation of the femur 152 that are within a distance from theassociated transformed control point. The plurality of points from therepresentation of the femur 152 are adjusted (460) based on the distanceand direction.

The three-dimensional representation of the femur 152 can be made up ofgeometrical shapes. For example, if the representation of the femur 152is created with triangles, a group of triangles on the representation ofthe femur 152 which are closest to the transformed control point aredetermined. Each vertex in the group is adjusted using the cartilagedistance and direction to form an area representing cartilage 360. Thegeometrical shapes of three-dimensional representation of the femur 152can be a set of polygons. Each of the plurality of points of therepresentation of the femur 152 can correspond to a set of polygons fromthe superset of polygons that make up the representation of the femur152. The transformed control points can be registered to the closestpoints on the areas representing cartilage 360 using, for example, apaired-point registration algorithm. Geometrical shapes can be used torepresent any component (e.g., patello-femoral implant component 154,medial implant component 156, and/or lateral implant component 158).

The final registration to the areas representing cartilage 360 can besuitably constrained (e.g., around an axis) to automatically adjust theposition of one implant relative to another. For example, if therepresentation of the patello-femoral implant component 154 is adjustedbased on the generated areas representing cartilage 360, therepresentation of the medial implant component 156 can be automaticallyadjusted to coincide with the adjustment of the representation of thepatello-femoral implant component 154. Advantageously, all implantcomponents can be adjusted to account for the generation of areasrepresenting cartilage around one implant component.

FIGS. 9A-9D illustrate bone points along a femur 500 for implantplanning. The femur includes a mechanical axis 502, anatomic axis 504 at4° from the mechanical axis 502, and anatomic axis 506 at 6° from themechanical axis 502. Bone 500 includes bone points F1 through F10. Bonepoints F1-F10 can be extreme points of the femur 500. The bone pointscan represent, for example:

-   -   F1—Most anterior medial point;    -   F2—Most anterior lateral point;    -   F3—Most distal medial point;    -   F4—Most distal lateral point;    -   F5—Most posterior medial point;    -   F6—Most posterior lateral point;    -   F7—Most anterior trochlear groove;    -   F8—Most distal trochlear groove;    -   F9—Medial epicondyle; and    -   F10—Lateral epicondyle.

The femur 500 can also include points F14 and F15 (not shown), where F14is at the midpoint between F 1 and F5, and point F15 is at the midpointbetween F2 and F6. Bone points F3 and F4 make up the distal condylaraxis (DCA) 508. The DCA 508 is approximately 3° from horizontal 510. F7and F8 represent the Anterior-posterior axis (AP axis) 512. F9 and F10represent the Transepicondylar axis (TEA) 514. The TEA 514 isperpendicular to the AP axis 512. F5 and F6 make up the posteriorcondylar axis (PCA) 516. The PCA 516 is approximately 3° from a line 518that is parallel to the TEA 514.

FIGS. 10A-10C illustrate implant points on implant components of amultiple component implant 600 (i.e., the patello-femoral implantcomponent 154, the medial implant component 156, and the lateral implantcomponent 158) for implant planning. The implant points include pointsC1-C15. The implant points can represent, for example:

-   -   C1—Most anterior medial point;    -   C2—Most anterior lateral point;    -   C3—Most distal medial point;    -   C4—Most distal lateral point;    -   C5—Most posterior medial point;    -   C6—Most posterior lateral point;    -   C7—Most anterior trochlear groove;    -   C8—Most distal trochlear groove;    -   C9—Center of medial transition arc;    -   C10—Center of lateral transition arc;    -   C11—Medial transition location;    -   C12—Lateral transition location;    -   C13—Superior transition location;    -   C14—Midpoint between points C1 and C5; and    -   C15—Midpoint between points C2 and C6.

Point C9 lies on the primary articular surface with the same X and Yvalue as the internal edge arc center of the medial femoral implantcomponent (i.e., the medial implant component 156). C10 lies on theprimary articular surface with the same X and Y value as the internaledge arc center of the lateral femoral implant component (i.e., thelateral implant component 158). C11 lies on the primary articularsurface, the midplane between the lateral edge of the medial femoralimplant component and the medial edge of the patello-femoral implantcomponent 154, and the midplane between the anterior tip of the medialfemoral implant component and the posterior tip of the patello-femoralimplant component 154. C11 can serve as the location forupsizing/downsizing femoral or patello-femoral implant components. C12lies on the primary articular surface, the midplane between the medialedge of the lateral femoral implant component and the lateral edge ofthe patello-femoral implant component 154, and the midplane between theanterior tip of the lateral femoral implant component and the posteriortip of the patello-femoral implant component 154. C12 can also serve asthe location for upsizing/downsizing femoral or patello-femoralcomponents. C13 lies on a surface that is midway between the articularsurface and the backside surface (1.5 mm offset from primary articularsurface), on the outer profile of the patello-femoral implant component154, on the trochlear groove pathway. C14 is the midpoint between themost anterior and most posterior medial points. C14 can be used inpre-operative planning. C15 is the midpoint between the most anteriorand most posterior lateral points. C15 can be used in pre-operativeplanning.

FIGS. 11A-11C illustrate implant component axes relative to the implantcomponents of a multiple component implant 600 (i.e., thepatello-femoral implant component 154, the medial implant component 156,and the lateral implant component 158) for implant planning. The axescan include axes A1-A15, which can represent, for example:

-   -   A1—Medial medial-lateral (ML) axis (x-axis) through point C1l        (e.g., flexion/extension);    -   A2—Medial anterior-posterior (AP) axis (y-axis) through point        C1l (e.g., varus/valgus);    -   A3—Medial superior-inferior (SI) axis (z-axis) through point C9        (e.g., internal/external);    -   A4—Patello-femoral (PFJ) superior ML axis (x-axis) through point        C13 (e.g., flexion/extension);    -   A5—Axis through points C11 and C13;    -   A6—SI axis (z-axis) through point C8 (e.g., internal/external);    -   A7—SI axis (z-axis) through point C13 (e.g., internal/external);    -   A8—SI axis (z-axis) through midpoint of C8 and C13 (e.g.,        internal/external);    -   A9—Axis through points C8 and C13;    -   A10—Lateral ML axis (x-axis) through point C12 (e.g.,        flexion/extension);    -   A11—Lateral AP axis (y-axis) through point C12 (e.g.,        varus/valgus);    -   A12—Lateral SI axis (z-axis) through point C10 (e.g.,        internal/external);    -   A13—Axis through points C12 and C13;    -   A14—SI axis (z-axis) through C14 (e.g., internal/external); and    -   A15—AP axis (y-axis) through point C8 (e.g., varus/valgus).

For pre-operation planning, cartilage points can be assumed. Thesecartilage points can include:

-   -   F1′—Most anterior medial point+1 mm in the Y direction;    -   F2′—Most anterior lateral point+1 mm in the Y direction;    -   F3′—Most distal medial point−2 mm in the Z direction;    -   F4′—Most distal lateral point−2 mm in the Z direction;    -   F5′—Most posterior medial point−2 mm in the Y direction;    -   F6′—Most posterior lateral point−2 mm in the Y direction;    -   F7′—Most anterior trochlear groove+2 mm in the Y direction;    -   F8′—Most distal trochlear groove−2 mm in the Z direction;    -   F14′—Midpoint between F1′ and F5′; and    -   F15′—Midpoint between F2′ and F6′.

Mapped transition points can be taken (e.g., manually with a probe). Anynumber of mapped transition points can be used. These points, for afemur for example, can include:

-   -   M1—Most anterior medial point mapped on cartilage near C1;    -   M2—Most anterior lateral point mapped on cartilage near C2;    -   M7—Most anterior trochlear point mapped on cartilage near C7;    -   M8—Most distal trochlear groove mapped on cartilage near C8;    -   M11—Medial transition mapped on cartilage near C11;    -   M12—Lateral transition mapped on cartilage near C12; and    -   M13—Superior transition mapped on bone near C13.

In some embodiments, a tibial onlay or inlay implant component (e.g., anarticular surface) can be calculated. The tibial onlay or inlay implantcomponent can include, for example:

-   -   P000—a poly centroid at 0° flexion mapped into femoral implant        space;    -   P090—a poly centroid at 90° flexion mapped into femoral implant        space; and    -   PXXX—any other poly centroid at XXX° flexion mapped into femoral        implant space.

Such onlays or inlays can provide, for example, a relationship betweenthe tibia and the femur. Advantageously, this can prevent positioning ofthe implant components in a way that adversely affects the tibia (e.g.,causing excessive tightening).

Preoperative Planning

The following is one example of preoperative planning. Preoperativeplanning can include acquiring the hip center and ankle center of thepatient. Bounding box bone landmarks (e.g., for the femur and tibia,such as points F1-F10) are acquired. The bones of interest areorientated, and the bounding box bone landmarks can be re-acquired basedon the final orientation. A proper implant size is selected from thevariety of sizes available to the system 100. In some embodiments, aproper implant size is calculated by computing the anterior-posterior(AP) distance as the AY between points F1′ and F5′. This will bedescribed for a three component implant. A three component implant maybe, for example, a tricompartmental implant that includes an implantcomponent for each of the three compartments of the joint (e.g., themedial compartment, the lateral compartment, and the patello-femoralcompartment). For example, a tricompartmental implant can include thepatello-femoral implant component, the medial femoral implant component,and the lateral femoral implant component. A three component implant mayalso be an implant that includes three components that are implanted inone or more compartments of the joint (e.g., the medial compartment, thelateral compartment, and/or the patello-femoral compartment). Forexample, the patello-femoral implant component can be split into threesegmented components that are each implanted in the patello-femoralcompartment of the joint. In another example, the patello-femoralimplant component 154 could be split into two segmented components thatare used in combination with one other implant component (e.g., themedial or lateral femoral implant component). In this example, the threecomponent implant is a tricompartmental implant that includes thepatello-femoral implant component (e.g., represented by representation154), the medial implant component (e.g., represented by representation156), and the lateral implant component (e.g., represented byrepresentation 158). For the tricompartmental implant, a size isselected that best matches this distance (ΔY between points C1 and C5)by finding the size that has the minimum difference. The system 100displays the three component implant, in this example, atricompartmental implant.

A best fit is determined for the tricompartmental implant to points F1′through F8′. In some embodiments, a best fit is found by performing anumber of steps: (1) translate the tricompartmental implant such thatC14 is at the same location as F14′, (2) rotate the tricompartmentalimplant about axis A14 until C15 has the same y-value as F15′, (3)translate in the medial-lateral (ML) direction until the midpoint ofC1-C2 has the same x-value as the midpoint of F1′-F2′ (or until C8 hassame x-value as F8′), (4) translate in the superior-inferior (SI)direction until C8 has the same z-value as F8′, (5) rotate about axisA15 until AZ between points C3 and F3′ is equal to AZ between points C4and F4′, (6) repeat until changes are insignificant.

Intraoperative Planning

The following is an exemplary example of steps that can be performedduring intraoperative planning. During the operation, the patient's boneis registered, as described, for example, in U.S. Patent Publication2006/0142657, published Jun. 29, 2006, which is hereby incorporated byreference herein in its entirety. Bone poses can be captured, forexample, at 0°, 90°, and other angles. Transition region points arecaptured (e.g., medial cartilage transition, lateral cartilagetransition, superior bone transition, and/or the like).

An implant size is calculated for the patient. The system 100 computesthe AP distance by, for example, computing the ΔY between points M13 andP090. The system 100 selects the tricompartmental implant size by, forexample, determining the tricompartmental implant size that has aminimum difference from the ΔY between points C5 and C13. The system 100can display a representation of the selected tricompartmental implant(e.g., through display 108 of FIG. 1).

The system 100 fits the implant to pose capture and transition regionacquisition points.

For example, the system 100 or a user can move (e.g., rotate, translate,etc.) the patello-femoral implant component (e.g., the representation154) to a desired orientation and location. In some examples, thefemoral components (e.g., the representations 156, 158) move linked tothe patello-femoral implant component. In some examples, thepatello-femoral implant component can be automatically fit to the bonewith movements (e.g., rotations, translations, etc.) to match thepatello-femoral implant component to the mapped points (e.g., the mappedtransition points M1, M2, M7, M8, M11, M12, M13).

Other computer operations can be performed, such as a fit to the femoralcondyle of the femur or a fit to all portions of the bone. This will bedescribed for a two component implant. A two component implant may be,for example, a bicompartmental implant that includes an implantcomponent for two of the three compartments of the joint (e.g., themedial compartment, the lateral compartment, the patello-femoralcompartment). For example, a bicompartmental implant can include thepatello-femoral implant component and either the medial femoral implantcomponent or the lateral femoral implant component. In another example,a bicompartmental implant can include the medial and lateral femoralimplant components. A two component implant may also be an implant thatincludes two components that are implanted in one compartment of thejoint (e.g., the medial compartment, the lateral compartment, or thepatello-femoral compartment). For example, the patello-femoral implantcomponent can be split into two segmented components that are eachimplanted in the patello-femoral compartment of the joint. In thisexample, the two component implant is a bicompartmental implant thatincludes the patello-femoral implant component (e.g., the representation154) and the medial implant component (e.g., the representation 156).The bicompartmental implant AP can be moved so that C13 has the samey-value as M13. The bicompartmental implant SI can be moved so that C8has the same z-value as M8. The femoral component internal-external (IE)can be rotated about axis A3 until the x-value of C5 matches the x-valueof P090. The femoral component flexion-extension (FE) can be rotatedabout axis A1 until the z-value of C3 matches the z-value of P000.

The posterior gap can be calculated and/or displayed by measuring the ΔYbetween points C5 and P090. The system 100 can determine the fit (e.g.,if there is a gap/loose or if there is an overlap/tight). If the system100 determines the posterior gap is loose, the length can be increased.To increase length, for example, the bicompartmental implant can beflexed about axis A4. The system 100 can determine the rotation anglevalue for each size that approximately yields a 0.5 mm length increase.To decrease length, the bicompartmental implant can be extended aboutaxis A4. The system 100 can determine the rotation angle value for eachsize that approximately yields a 0.5 mm length increase. The user can,for example, click the display to adjust the length by a predeterminedamount (e.g., increase/decrease the length by 0.5 mm). Any number ofthese steps can be repeated one or more times to achieve a desiredposterior gap.

Adjustments can be made to the femoral component (e.g., the medialimplant component 156 or the lateral implant component 158). Forexample, the varus/valgus can be adjusted to fit the bone, theflexion/extension can be adjusted to change the extension gap, and anyother adjustment can be made. To increase or decrease a size of theimplant system or implant components (e.g., thefemoral/patello-femoral), a new component can be placed in at C11. Toupsize and/or downsize the femoral implant component when, for example,the bone has already been resected to include peg holes to receive thepegs (or posts) on the back of the femoral implant component and apocket to receive the body of the femoral implant component, the nextsized femoral implant component needs can be placed into position at thepeg axes at a predetermined depth. Tibial inlay and/or onlay implantcomponent articular surfaces can be matched. The system 100 cancalculate the angle change necessary to increase and/or decrease thesize of the bicompartmental implant. The tricompartmental implant can beautomatically fit to the bone, pose, transition, and/or the like. Whilethe above example was described with reference to the medial femoralimplant component, those skilled in the art can appreciate these systemsand methods can be extended to any multiple implant component system.

FIG. 12 shows an embodiment of an exemplary surgical system 710 in whichthe techniques described above can be implemented. Such an exemplarysystem is described in detail, for example, in U.S. Patent Publication2006/0142657, published Jun. 29, 2006, which is hereby incorporated byreference herein in its entirety. The surgical system 710 includes acomputing system 720, a haptic device 730, and a navigation system 40.In operation, the surgical system 710 enables comprehensive,intraoperative surgical planning. The surgical system 710 also provideshaptic guidance to a user (e.g., a surgeon) and/or limits the user'smanipulation of the haptic device 730 as the user performs a surgicalprocedure. Although included for completeness in the illustratedembodiment, the haptic device 730 and its associated hardware andsoftware is not necessary to perform the techniques described herein.

The computing system 720 includes hardware and software apparatus foroperation and control of the surgical system 710. Such hardware and/orsoftware apparatus is configured to enable the system 710 to perform thetechniques described herein. In FIG. 12, the computing system 720includes a computer 721, a display device 723, and an input device 725.The computing system 720 may also include a cart 729.

The computer 721 may be any known computing system but is preferably aprogrammable, processor-based system. For example, the computer 721 mayinclude a microprocessor, a hard drive, random access memory (RAM), readonly memory (ROM), input/output (I/O) circuitry, and any otherwell-known computer component. The computer 721 is preferably adaptedfor use with various types of storage devices (persistent andremovable), such as, for example, a portable drive, magnetic storage(e.g., a floppy disk), solid state storage (e.g., a flash memory card),optical storage (e.g., a compact disc or CD), and/or network/Internetstorage. The computer 721 may comprise one or more computers, including,for example, a personal computer (e.g., an IBM-PC compatible computer)or a workstation (e.g., a SUN or Silicon Graphics workstation) operatingunder a Windows, MS-DOS, UNIX, or other suitable operating system andpreferably includes a graphical user interface (GUI).

The display device 723 is a visual interface between the computingsystem 720 and the user. The display device 723 is connected to thecomputer 721 and may be any device suitable for displaying text, images,graphics, and/or other visual output. For example, the display device723 may include a standard display screen (e.g., LCD, CRT, plasma,etc.), a touch screen, a wearable display (e.g., eyewear such as glassesor goggles), a projection display, a head-mounted display, a holographicdisplay, and/or any other visual output device. The display device 723may be disposed on or near the computer 721 (e.g., on the cart 729 asshown in FIG. 12) or may be remote from the computer 721 (e.g., mountedon a wall of an operating room or other location suitable for viewing bythe user). The display device 723 is preferably adjustable so that theuser can position/reposition the display device 723 as needed during asurgical procedure. For example, the display device 723 may be disposedon an adjustable arm (not shown) that is connected to the cart 729 or toany other location well-suited for ease of viewing by the user.

The display device 723 may be used to display any information useful fora medical procedure, such as, for example, images of anatomy generatedfrom an image data set obtained using conventional imaging techniques,graphical models (e.g., CAD models of implants, instruments, anatomy,etc.), graphical representations of a tracked object (e.g., anatomy,tools, implants, etc.), constraint data (e.g., axes, articular surfaces,etc.), representations of implant components, digital or video images,registration information, calibration information, patient data, userdata, measurement data, software menus, selection buttons, statusinformation, and the like. In some examples, the display device 723displays the two dimensional and/or three dimensional displays asillustrated in FIGS. 2, 4A-4B, 5, and 6.

In addition to the display device 723, the computing system 720 mayinclude an acoustic device (not shown) for providing audible feedback tothe user. The acoustic device is connected to the computer 721 and maybe any known device for producing sound. For example, the acousticdevice may comprise speakers and a sound card, a motherboard withintegrated audio support, and/or an external sound controller. Inoperation, the acoustic device may be adapted to convey information tothe user. For example, the computer 721 may be programmed to signal theacoustic device to produce a sound, such as a voice synthesized verbalindication “DONE,” to indicate that a step of a surgical procedure iscomplete. Similarly, the acoustic device may be used to alert the userto a sensitive condition, such as producing a beep to indicate that asurgical cutting tool is nearing a critical portion of soft tissue.

The input device 725 of the computing system 720 enables the user tocommunicate with the surgical system 710. The input device 725 isconnected to the computer 721 and may include any device enabling a userto provide input to a computer. For example, the input device 725 can bea known input device, such as a keyboard, a mouse, a trackball, a touchscreen, a touch pad, voice recognition hardware, dials, switches,buttons, a trackable probe, a foot pedal, a remote control device, ascanner, a camera, a microphone, and/or a joystick. For example, theinput device 725 allows a user to move one or more components displayedon display device 723 based on one or more constraints, as describedabove, for planning the implant installation.

The computing system 720 is coupled to a computing device 731 of thehaptic device 730 via an interface 7100 a and to the navigation system40 via an interface 100 b. Interfaces 7100 a and 100 b can include aphysical interface and a software interface. The physical interface maybe any known interface such as, for example, a wired interface (e.g.,serial, USB, Ethernet, CAN bus, and/or other cable communicationinterface) and/or a wireless interface (e.g., wireless Ethernet,wireless serial, infrared, and/or other wireless communication system).The software interface may be resident on the computer 721, thecomputing device 731, and/or the navigation system 40. In someembodiments, the computer 721 and the computing device 731 are the samecomputing device.

The surgical system 710 has additional features as described in U.S.patent application Ser. No. 11/963,547, filed Dec. 21, 2007, which ishereby incorporated by reference herein in its entirety. In someexamples, the surgical system 710 allows a user to plan the installationof a multiple component implant in a patient using the computing system720. The user, for example, uses the input device 725 to position (e.g.,rotate, translate, shift, etc.) one or more components of a multiplecomponent implant based on one or more constraints to properly fit theunique anatomy of the patient. The planning procedure, once completed,is transmitted to and/or used by the haptic device 730 via interface7100 a to assist a surgeon during the bone preparation and implantinstallation procedure.

In some examples, the haptic device 730 is the Tactile Guidance System™(TGS™) manufactured by MAKO Surgical Corp., which is used to prepare thesurface of the patient's bone for insertion of the implant system. Thehaptic device 730 provides haptic (or tactile) guidance to guide thesurgeon during a surgical procedure. As described in U.S. PatentPublication 2006/0142657, published Jun. 29, 2006, which is herebyincorporated by reference herein in its entirety, the haptic device isan interactive surgical robotic arm that holds a surgical tool (e.g., asurgical burr) and is manipulated by the surgeon to perform a procedureon the patient, such as cutting a surface of a bone in preparation forimplant installation. As the surgeon manipulates the robotic arm to movethe tool and sculpt the bone, the haptic device 730 guides the surgeonby providing force feedback that constrains the tool from penetrating avirtual boundary.

For example, the surgical tool is coupled to the robotic arm andregistered to the patient's anatomy. The surgeon operates the tool bymanipulating the robotic arm to move the tool and perform the cuttingoperation. As the surgeon cuts, an optical camera 41 of the navigationsystem 40 tracks the location of the tool and the patient's anatomy. Thepatient's anatomy can be tracked, for example, by attaching a trackingarray 43 a to the patient's femur F and a tracking array 43 b to thepatient's tibia T, as shown in FIG. 12. The tracking arrays 43 a, 43 bare detectable by the optical camera 41. In most cases, the hapticdevice 730 allows the surgeon to freely move the tool in the workspace.However, when the tool is in proximity to the virtual boundary (which isalso registered to the patient's anatomy), the haptic device 730controls the haptic device to provide haptic guidance (e.g., forcefeedback) that tends to constrain the surgeon from penetrating thevirtual boundary with the tool.

The virtual boundary may represent, for example, a cutting boundarydefining a region of bone to be removed or a virtual pathway for guidingthe surgical tool to a surgical site without contacting criticalanatomical structures. The virtual boundary may be defined by a hapticobject (e.g., one or more haptic objects, as described below in furtherdetail), and the haptic guidance may be in the form of force feedback(i.e., force and/or torque) that is mapped to the haptic object andexperienced by the surgeon as resistance to further tool movement in thedirection of the virtual boundary. Thus, the surgeon may feel thesensation that the tool has encountered a physical object, such as awall. In this manner, the virtual boundary functions as a highlyaccurate virtual cutting guide. For example, the virtual boundary canrepresent a region of cartilage and/or bone to be removed for properlyfitting the medial, lateral, and patello-femoral implant components tothe patient's femur as planned through the implant planning proceduredescribed above. Such virtual boundaries can help to ensure theefficient and accurate removal of portions of a patient's anatomy toaccurately fit implant components based on a customized implant planningfor the patient. This also ensures that the actual placement of theimplant components meets the constraints that were used in planning theplacement of each of the physically separate implant components.

In some examples, the haptic device 730 includes a visual display (e.g.,the display device 723 shown in FIG. 12) showing the amount of boneremoved during the cutting operation. Because the haptic device 730utilizes tactile force feedback, the haptic device 730 can supplement orreplace direct visualization of the surgical site and enhance thesurgeon's natural tactile sense and physical dexterity. Guidance fromthe haptic device 730 coupled with computer aided surgery (CAS), enablesthe surgeon to actively and accurately control surgical actions (e.g.,bone cutting) to achieve the tolerances and complex bone resectionshapes that enable optimal and customized installation of implants.

In addition to bone preparation, a CAS system enables the surgeon tocustomize the placement of the implant components to construct aprosthetic device tailored to the specific needs of the patient based onthe patient's unique anatomy, ligament stability, kinematics, and/ordisease state. Implant planning may be accomplished preoperatively orintraoperatively and may be evaluated and adjusted in real time duringexecution of the surgical procedure. In a preferred embodiment, implantplanning is accomplished using the surgical system 710. For example, asdescribed above, the surgeon may use the surgical planning features ofthe computing system 720 to plan the placement of representations ofeach implant component relative to a preoperative CT image (or otherimage or model of the anatomy). The software enables the surgeon to viewthe placement of each component relative to the anatomy (e.g., bone,articular cartilage surfaces, and/or the like) and to other components,as described, for example, in U.S. Patent Publication 2006/0142657,published Jun. 29, 2006, which is hereby incorporated by referenceherein in its entirety. Further, the software enables the surgeon toview constraints associated with the placement of each component (e.g.,articular surfaces, axes of constraint, and/or the like). The softwaremay also be configured to illustrate how the components will interact asthe joint moves through a range of motion. Based on the componentplacement selected by the surgeon, the haptic device 730 softwaregenerates one or more haptic objects, which create one or more virtualboundaries representing, for example, a portion of bone to be removed orcritical anatomy to be avoided based at least in part on the placementof the implant components. During surgery, the haptic object isregistered to the patient's anatomy. By providing force feedback, thehaptic device 730 enables the surgeon to interact with the haptic objectin the virtual environment. In this manner, the haptic device 730haptically guides the surgeon during bone preparation to sculpt orcontour the appropriate location of the bone so that a shape of the bonesubstantially conforms to a shape of a mating surface of a component ofthe multiple component implant. For example, a haptic object can becreated to represent the portion of the bone and/or cartilage area to beremoved for implanting the medial femoral implant component (e.g.,represented by the representation 156).

In a preferred embodiment, the haptic device 730 is used by the surgeonto preoperatively plan implant placement using computer simulation toolsto determine whether the preoperative plan will result in the desiredclinical results (e.g., using constraints). Then, during surgery, thesurgeon may query the soft tissue and ligaments as the joint is movedthrough a range of motion using appropriate instrumentation and sensorsas is well known. This information may be combined with the computersimulation information of the haptic device 730 to adjust the implantplanning and/or suggest to the surgeon potential changes and adjustmentsto implant placement that may achieve the desired clinical outcomes.

The above-described systems and methods can be implemented in digitalelectronic circuitry, in computer hardware, firmware, and/or software.The implementation can be as a computer program product (i.e., acomputer program tangibly embodied in an information carrier). Theimplementation can, for example, be in a machine-readable storagedevice, for execution by, or to control the operation of, a dataprocessing apparatus. The implementation can, for example, be aprogrammable processor, a computer, and/or multiple computers.

A computer program can be written in any form of programming language,including compiled and/or interpreted languages, and the computerprogram can be deployed in any form, including as a stand-alone programor as a subroutine, element, and/or other unit suitable for use in acomputing environment. A computer program can be deployed to be executedon one computer or on multiple computers at one site.

Method steps can be performed by one or more programmable processorsexecuting a computer program to perform functions of the invention byoperating on input data and generating output. Method steps can also beperformed by and an apparatus can be implemented as special purposelogic circuitry. The circuitry can, for example, be a FPGA (fieldprogrammable gate array) and/or an ASIC (application-specific integratedcircuit). Modules, subroutines, and software agents can refer toportions of the computer program, the processor, the special circuitry,software, and/or hardware that implements that functionality.

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andany one or more processors of any kind of digital computer. Generally, aprocessor receives instructions and data from a read-only memory or arandom access memory or both. The essential elements of a computer are aprocessor for executing instructions and one or more memory devices forstoring instructions and data. Generally, a computer can include, can beoperatively coupled to receive data from and/or transfer data to one ormore mass storage devices for storing data (e.g., magnetic,magneto-optical disks, or optical disks).

Data transmission and instructions can also occur over a communicationsnetwork. Information carriers suitable for embodying computer programinstructions and data include all forms of non-volatile memory,including by way of example semiconductor memory devices. Theinformation carriers can, for example, be EPROM, EEPROM, flash memorydevices, magnetic disks, internal hard disks, removable disks,magneto-optical disks, CD-ROM, and/or DVD-ROM disks. The processor andthe memory can be supplemented by, and/or incorporated in specialpurpose logic circuitry.

To provide for interaction with a user, the above described techniquescan be implemented on a computer having a display device. The displaydevice can, for example, be a cathode ray tube (CRT) and/or a liquidcrystal display (LCD) monitor. The interaction with a user can, forexample, be a display of information to the user and a keyboard and apointing device (e.g., a mouse or a trackball) by which the user canprovide input to the computer (e.g., interact with a user interfaceelement). Other kinds of devices can be used to provide for interactionwith a user. Other devices can, for example, be feedback provided to theuser in any form of sensory feedback (e.g., visual feedback, auditoryfeedback, or tactile feedback). Input from the user can, for example, bereceived in any form, including acoustic, speech, and/or tactile input.

The above described techniques can be implemented in a distributedcomputing system that includes a back-end component. The back-endcomponent can, for example, be a data server, a middleware component,and/or an application server. The above described techniques can beimplemented in a distributing computing system that includes a front-endcomponent. The front-end component can, for example, be a clientcomputer having a graphical user interface, a Web browser through whicha user can interact with an example implementation, and/or othergraphical user interfaces for a transmitting device. The components ofthe system can be interconnected by any form or medium of digital datacommunication (e.g., a communication network). Examples of communicationnetworks include a local area network (LAN), a wide area network (WAN),the Internet, wired networks, and/or wireless networks.

The system can include clients and servers. A client and a server aregenerally remote from each other and typically interact through acommunication network. The relationship of client and server arises byvirtue of computer programs running on the respective computers andhaving a client-server relationship to each other.

Packet-based networks can include, for example, the Internet, a carrierinternet protocol (IP) network (e.g., local area network (LAN), widearea network (WAN), campus area network (CAN), metropolitan area network(MAN), home area network (HAN)), a private IP network, an IP privatebranch exchange (IPBX), a wireless network (e.g., radio access network(RAN), 802.11 network, 802.16 network, general packet radio service(GPRS) network, HiperLAN), and/or other packet-based networks.Circuit-based networks can include, for example, the public switchedtelephone network (PSTN), a private branch exchange (PBX), a wirelessnetwork (e.g., RAN, bluetooth, code-division multiple access (CDMA)network, time division multiple access (TDMA) network, global system formobile communications (GSM) network), and/or other circuit-basednetworks.

The transmitting device can include, for example, a computer, a computerwith a browser device, a telephone, an IP phone, a mobile device (e.g.,cellular phone, personal digital assistant (PDA) device, laptopcomputer, electronic mail device), and/or other communication devices.The browser device includes, for example, a computer (e.g., desktopcomputer, laptop computer) with a world wide web browser (e.g.,Microsoft® Internet Explorer® available from Microsoft Corporation,Mozilla® Firefox available from Mozilla Corporation). The mobilecomputing device includes, for example, a personal digital assistant(PDA).

Comprise, include, and/or plural forms of each are open ended andinclude the listed parts and can include additional parts that are notlisted. And/or is open ended and includes one or more of the listedparts and combinations of the listed parts.

One skilled in the art will realize the invention may be embodied inother specific forms without departing from the spirit or essentialcharacteristics thereof. The foregoing embodiments are therefore to beconsidered in all respects illustrative rather than limiting of theinvention described herein. Scope of the invention is thus indicated bythe appended claims, rather than by the foregoing description, and allchanges that come within the meaning and range of equivalency of theclaims are therefore intended to be embraced therein.

What is claimed is:
 1. A surgical planning computerized method,comprising: registering a joint of a patient in physical space with amodel of the joint in virtual space; planning placement of an implant tobe implanted in the joint, wherein a planned placement of the implant isdetermined by: performing a soft tissue assessment of the joint; andautomatically fitting the implant relative to at least one of a bone ofthe joint, a second implant, a cartilage of the patient, or based on aligament characteristic of the patient; and generating at least onevirtual boundary based on the planned placement of the implant in thejoint, the at least one virtual boundary configured to control movementof a surgical tool while the tool is being used to prepare the joint toreceive the implant in the planned placement.
 2. The method of claim 1,wherein performing the soft tissue assessment comprises assessment of atleast one of a ligament or the cartilage of the patient.
 3. The methodof claim 2, wherein the assessment of the ligament of the patientcomprises moving the joint through a range of motion and capturinginformation related to a pose of one or more bones of the joint as thejoint is moved through the range of motion.
 4. The method of claim 2,wherein assessment of cartilage comprises capturing a plurality ofmeasured cartilage points in the joint and mapping the measuredcartilage points to the model of the joint in virtual space.
 5. Themethod of claim 1, wherein the planned placement of the implant isdetermined by automatically fitting the implant relative to the bone ofthe joint, the second implant, the cartilage of the patient, and basedon the ligament characteristic of the patient.
 6. The method of claim 5,wherein fitting the implant relative to the bone of the joint comprisesselecting an implant having a size and shape providing a best fit forthe joint.
 7. The method of claim 6, further comprising positioning theimplant using a constraint associated with the model of the joint,wherein the constraint comprises at least one of an axis of rotation oran axis of translation.
 8. The method of claim 5, wherein fitting theimplant relative to the second implant comprises using a constraintassociated with the second implant, wherein the constraint comprises atleast one of an axis of rotation or an axis of translation.
 9. Themethod of claim 5, wherein fitting the implant relative to the cartilagecomprises: capturing a plurality of measured cartilage points in thejoint; mapping the measured cartilage points to the model of the jointin virtual space; and planning placement of the implant by aligning theimplant with the measured cartilage points.
 10. The method of claim 9,wherein mapping the measured cartilage points comprises mappingtransition points, wherein the transition points are points on thecartilage that are in proximity to control points on the implant. 11.The method of claim 9, wherein planning placement of the implantcomprises adjusting the implant along at least one of an axis ofrotation or an axis of translation to align the implant with themeasured cartilage points.
 12. The method of claim 5, wherein fittingthe implant based on the ligament characteristic comprises determining agap in the joint as the joint is moved through a range of motion andadjusting the planned placement of the implant along at least one of anaxis of rotation or an axis of translation to result in a desired gap inthe joint through the range of motion.
 13. The method of claim 1,wherein the at least one virtual boundary is configured to controlmovement of the surgical tool by providing haptic feedback to a user asthe user manipulates the tool.
 14. A surgical planning system,comprising: a computer configured to: register a joint of a patient inphysical space with a model of the joint in virtual space; planplacement of an implant to be implanted in the joint, wherein a plannedplacement of the implant is determined by: performing a soft tissueassessment of the joint; and automatically fitting the implant relativeto at least one of a bone of the joint, a second implant, a cartilage ofthe patient, or based on a ligament characteristic of the patient; andgenerate at least one virtual boundary based on the planned placement ofthe implant in the joint, the at least one virtual boundary configuredto control movement of a surgical tool while the tool is being used toprepare the joint to receive the implant in the planned placement. 15.The system of claim 14, wherein the computer is further configured toperform the soft tissue assessment by performing an assessment of aligament, and wherein the assessment of the ligament comprises movingthe joint through a range of motion and capturing information, from atracking system, related to a pose of one or more bones of the joint asthe joint is moved through the range of motion.
 16. The system of claim14, wherein the computer is further configured to perform the softtissue assessment by performing an assessment of cartilage, wherein theassessment of cartilage comprises receiving information from a trackedprobe associated with a plurality of measured cartilage points in thejoint, and mapping the measured cartilage points to the model of thejoint in virtual space.
 17. The system of claim 14, wherein the computeris further configured to fit the implant relative to the bone of thejoint by selecting an implant having a size and shape providing a bestfit for the joint and positioning the implant using a constraintassociated with the model of the joint, wherein the constraint comprisesat least one of an axis of rotation or an axis of translation.
 18. Thesystem of claim 14, wherein the computer is further configured to fitthe implant relative to the second implant by using a constraintassociated with the second implant, wherein the constraint comprises atleast one of an axis of rotation or an axis of translation.
 19. Thesystem of claim 14, wherein fitting the implant relative to thecartilage comprises: capturing a plurality of measured cartilage pointsin the joint; mapping the measured cartilage points to the model of thejoint in virtual space; planning placement of the implant by aligningthe implant with the measured cartilage points; and adjusting theimplant along at least one of an axis of rotation or an axis oftranslation to align the implant with the measured cartilage points. 20.The system of claim 19, wherein mapping the measured cartilage pointscomprises mapping transition points, wherein the transition points arepoints on the cartilage that are in proximity to control points on theimplant.
 21. The system of claim 14, wherein the computer is furtherconfigured to fit the implant based on the ligament characteristic bydetermining a gap in the joint as the joint is moved through a range ofmotion and adjusting the planned placement of the implant along at leastone of an axis of rotation or an axis of translation to result in adesired gap in the joint through the range of motion.